1. Field of the Invention
The present invention relates to a plating apparatus and a method of cleaning a substrate holder, and more particularly to a dip-type plating apparatus in which a substrate, such as a semiconductor wafer, held by a substrate holder is immersed in a plating solution to form e.g., connecting bumps or interconnects on a surface of the substrate, and to a method for cleaning a substrate holder for use in such a plating apparatus.
2. Description of the Related Art
Electroplating is widely used to form connecting bumps at predetermined positions on a surface of a substrate, such as a semiconductor wafer. As shown in FIGS. 1 and 2, a substrate W is prepared with a seed layer 200 formed as a feeding layer on the substrate surface, a resist 202 coating the surface of the seed layer 200, and openings 202a formed at predetermined positions in the resist 202. While sealing a peripheral portion of the surface of the substrate W with a sealing member 204 mounted to a substrate holder, a plating area A of the substrate surface, surrounded by the sealing member 204, is brought into contact with a plating solution. A metal 206, which is used as bumps, is formed by plating on exposed surfaces of the seed layer 200, lying inside the resist openings 202a in the plating area A.
When the peripheral portion of the surface of the substrate W is sealed with the sealing member 204 of the substrate holder in this manner, the sealing member 204 may bridge over those resist openings 202 which lie in the peripheral portion of the surface of the substrate W. This would generally be unavoidable because of the necessity for securing the largest possible effective surface area of the substrate W. When the metal 206 is formed in the openings 202a over which the sealing member 204 bridges, the metal 206 may be deposited abnormally and reach a top surface of the resist 202, resulting in adhesion of an over-deposited metal 207 to the sealing member 204. The metal 207 adhering to the sealing member 204 grows every time plating of a substrate is performed.
If the substrate holder is used continuously with the metal 207 left on the sealing member 204, there will be a deficiency of a thickness or poor in-plane uniformity of a metal film formed on a substrate surface. Furthermore, leakage of a plating solution can occur when the plating area A of the substrate surface, surrounded by the sealing member 204, is immersed in the plating solution. It is therefore necessary to clean the substrate holder, periodically or as needed, to remove the metal 207 from the sealing member 204.
When the substrate holder is used in plating of a substrate having no resist film formed on the substrate surface, the seed layer 200 directly contacts the sealing member 204 of the substrate holder. Therefore, the metal 207, abnormally deposited on the substrate surface, may adhere to the sealing member 204.
In common practice, therefore, during maintenance work of the substrate holder, the substrate holder is cleaned manually, or with a cleaning liquid (chemical liquid) capable of dissolving the metal 207. Upon the maintenance work, in general, the substrate holder is removed from the plating apparatus and cleaning of the substrate holder and periodic replacement of parts are carried out.
A cleaning apparatus for automatically cleaning a suspended jig has been proposed. The cleaning apparatus includes a film-removing solution bath, a water bath, an acid cleaning bath, etc. arranged in this order in a space in which the suspended jig is transported by a transport means (see Japanese Laid-Open Utility Model Publication No. 58-92374). A cleaning apparatus has been proposed which, instead of a common dip or immersion method, employs a jet method in which a cleaning liquid is jetted toward a cleaning object (see Japanese Laid-Open Utility Model Publication No. 61-159083). A workpiece transport system has been proposed which allows a pallet, holding workpieces, to pass through a water-cleaning section, and then immerses the pallet in a pool of water and stores the pallet therein so as to prevent drying and oxidation of the workpieces (see Japanese Laid-Open Patent Publication No. 63-166990). A liquid processing apparatus has been proposed in which a substrate holder, holding a substrate, is moved from a processing bath to a cleaning section, where the substrate holder is cleaned together with the processing surface of the substrate (see Japanese Laid-Open Patent Publication No. 2002-249896).
The applicant has proposed a plating apparatus having a substrate holder cleaning section for cleaning a substrate holder in an open state, not holding a substrate. The plating apparatus can automatically clean the substrate holder without removing it from the plating apparatus (see Japanese Laid-Open Patent Publication No. 2008-45179).
An operation of the plating apparatus needs to be stopped in order to remove the substrate holder from the apparatus and clean the substrate holder. Even if a spare substrate holder is provided, the plating apparatus needs to be stopped at least during replacement of the substrate holder, resulting in a lowered productivity of the plating apparatus. In addition, it is laborious to remove the substrate holder from the plating apparatus.
The above-mentioned patent documents are not directed to a technique for automatically cleaning a substrate holder when it is stored in a plating apparatus, i.e. without taking the substrate holder out of the plating apparatus.
When a substrate holder in an open state, not holding a substrate, is cleaned as described in the Japanese Laid-Open Patent Publication No. 2008-45179, an electrical contact which is kept in contact with a seed layer of a substrate to feed electricity to the seed layer, will become wet with a cleaning liquid. If an electrical contact in a wet state comes into contact with a seed layer of a substrate, the seed layer may dissolve at its contact portion with the electrical contact, leading to a decrease in the electrical conduction between the electrical contact and the seed layer. An electrical contact must therefore be in a dry state upon contact with a seed layer. Thus, a substrate holder with an electrical contact in a wet state cannot be used until the electrical contact becomes dry. It is generally quite difficult to dry the electrical contact, located inside the substrate holder, in a short time.
In a case of using a plating apparatus which is configured to perform multi-layer composite plating on a surface of a substrate held by the substrate holder, a metal 207 (see FIG. 2), composed of different types of metals, may be abnormally deposited on the sealing member of the substrate holder. In most cases, no common cleaning liquid can effectively dissolve and remove the metal 207 composed of different types of metals. Therefore, different types of cleaning liquids should be used to clean the substrate holder. However, a plurality of cleaning baths for the different types of cleaning liquids should be provided for removing the different types of metals abnormally deposited on the sealing member of the substrate holder, thus considerably increasing a footprint of the plating apparatus.